(1) FIELD OF THE INVENTION
The present invention relates to a theft detector apparatus used to detect illegal entry into a vehicle, and more particularly to a theft detector apparatus which prevents any circumvention of its working such as is possible in such theft detector apparatuses as can be circumvented when attempted entry into a vehicle by removing the key cylinder with its built-in lock switch and short-circuiting the lead wires connected to the key unlock switch in the cylinder.
(2) DESCRIPTION OF PRIOR ART
Conventional theft detector apparatuses work by detecting that a door etc. has been opened by a means other than a key, by which they judge that a theft has taken place, and sound an alarm. In other words, the conditions for this kind of apparatus to be set are that the door locking means must be locked and all the other possible openings into the car, such as the side doors, the rear door, the hatch, the trunk and so on securely closed as well. When the theft detector apparatus is set in this way, it will detect an illegal entry (theft) whenever a door or any of the other openings is opened by a means other than a key. On the basis of this it will sound an alarm by sounding the horn and switching on the head and tail lights.
However, this type of theft detector apparatus is set by locking the door even when the door is shut from the inside. Because of this, the apparatus suffers from the disadvantage that it will be activated and the alarm sounded when the occupant(s) try to get out of the vehicle.
In addition to this, the above-mentioned theft detector apparatus does not detect a theft when the door is simply unlocked using a means other than a key, but only does so when a door etc. is actually opened. As a result, if a means can be found to circumvent the switch etc. that senses whether or not the door is open, the door can be opened without activating the detector, a defect that leads to a loss of reliability.
Thus the inventor, as disclosed in the specifications of Japanese Patent Application No. 102839/1984, has developed a vehicle theft detector apparatus which cannot be set from within the car, and which also has improved reliability. This provides that after setting the locking means of either or both of the driver's door and the front passenger door to the locked position, the door can be locked from the outside by closing the door with the knob still in the open position, thus creating a `keyless lock.` It further provides that it can only be set when it receives `closed` signals from all of the openable parts, after first having received in succession an `off` signal from the ignition key switch, an `open` signal from at least one of the above-mentioned keyless locks, and locked signals from all of the door locking means. This means that it cannot be set from within the vehicle, and that as long as there is no unlock signal from a key, it will judge that a theft has taken place and sound the alarm if it receives one or more of the following signals: an open latch signal from a door or an opening part, or an unlock signal from any of the door locking means.
The lock and key unlock sensor of this conventional apparatus is arranged as shown in FIG. 5. In other words, the locking means 11 attached to the latch on the car door 10 on the car body is connected via a linking mechanism 12 to the manual door knob 13, and also via a linking mechanism 14 to the solenoid 15 of the magnetic lock, and again via a linking mechanism 16 to the door key cylinder 17. This solenoid 15 is arranged so as to be activated by the magnetic lock switch 18. As the door locking means 11 is arranged so that it can be operated by either the door lock knob 13, the magnetic lock switch 18 or the door cylinder 17, it can be locked and unlocked independently by any one of them. The arm 16a of the linking mechanism 16 pivots on the pivot 16, and its distal end is connected with the door cylinder 17 by the arm 16c. Thus the rotation of the cylinder 17 causes the arm 16c to move in an upward or downward direction. At the bottom of this arm 16a is provided a key unlock sensor constituted by a limit switch 6a. FIG. 5 shows arm 16a in an intermediate position, and in this position the keyhole 17a of the key cylinder 17 is as shown in FIG. 6 (A). When the door is unlocked by inserting the key into the keyhole 17a and turning it to the position shown in FIG. 6 (B), the arm 16a is moved by the arm 16c in the direction of the arrow 19 shown in FIG. 5, thus pushing the movable portion 20 of the limit switch to the position shown by the broken line in this Figure. It thus presses down on the sensor terminal 21 of the limit switch, which then outputs a key unlock signal.
However, the problem with the switch mechanism of this type of key unlock sensor is that if the key cylinder is removed from the outside of the door 10, the arm 16c of the link mechanism 16 can be clearly seen through the hole where the cylinder was, and if this arm 16c of the linking mechanism 16 is directly pressed down using a finger or some other means, the arm 16a will move downward in the direction of the arrow 19 in FIG. 5, rotating about the pivot 16b to press down the moving portion 20 onto, and thus activating the key unlock sensor 6a. This releases the theft detector apparatus, which means that such an action as removal of the cylinder renders the apparatus totally ineffective.